Cone calorimeter was employed to study the ignitability of common thermoplastics, and the numerical and linear regression methods were used to deduce the ignition model for intermediate thermal thickness. Then the ignition time data was analyzed with the deduced model to get the critical heat flux, ignition temperature and thermal properties for the studied materials.The results showed that the deduced critical heat flux and ignition temperatures agreed well with those from literature,which indicated that the model is applicable.